Abstract: In this study, the adsorption of phosphorus onto both crystal and amorphous iron oxides under different pH conditions (i.e. pH=5, 6 and 7) had been investigated using synthetic goethite and ferrihydrite as the materials, respectively. Both Langmuir and Freundlich models were employed to fit the experimental adsorption data to identify the best model. The experimental results showed that these two iron oxides had good adsorption capacity for phosphorus. The modeling results indicated that both models were able to adequately describe the adsorption for both materials, but the Langmuir model was more accurate. Furthermore, through comparison of the equilibrium adsorption quantity (Q_max), the adsorption constants (K_L, K_F, n) and the maximum buffering capacity (MBC) of two materials, it was found that adsorption capacity of phosphorus onto the ferrihydrite was higher than that of the goethite in each pH condition, and the adsorption capacity for both materials had a considerable reduction with increasing pH whereas the decline trend observed on the ferrihydrite was more pronounced.

Key words: iron oxides, phosphorus, isothermal adsorption